69 
The median and extreme ice data of the 70-year period of observations do not differ markedly from the 
statistical data of the 30-year normal period (Sztobryn, Stanistawczyk, Schmelzer, 1999). Possible 
trends in the development of various ice parameters during the 70-year period are briefly discussed 
below. 
♦ first ice ♦ last ice Linear (last ice) Linear (first ice) 
4.5 
<D 
19.4 
O 
4.4 
•*—> 
(/> 
ro 
20.3 
■O 
5.3 
c 
ro 
19.2 
•*—> 
(/> 
4.2 
s— 
20.1 
o 
5.1 
(/> 
<D 
•*—> 
(0 
21.12 
6.12 
Q 
21.11 
6.11 
Winter 
Figure 6.4. Beginning of freezing and end of ice season at the Ueckermunde station (Szczecin Lagoon) in 
the period 1929-2000 
■Mean first ice 
■Mean last ice 
<i) 31.3 
Q 1.12 
1929 -1940 1941 - 1950 1951 - 1960 1961 - 1970 1971 - 1980 1981 - 1990 1991 - 2000 
Figure 6.5. Variation of the 10-year mean values of first and last ice at the Ueckermunde station in the 
period 1929-2000 
Figure 6.4 shows the dates of first ice formation and last ice occurrence in all winters of the 1929-2000 
period. The winters of 1944/45 and 1945/46 (no data available) as well as 1973/74 and 1974/75 (no ice 
formation) have not been taken into account. The linear trend curves of both parameters have negative 
slopes, but that of first ice formation is much weaker than that for the end of the ice season. Evaluating 
these data, one can say that on average over the past 70 years there has been an almost unchanged 
trend for first ice formation in the second decade of December, while the last ice on average disappears 
earlier and earlier. This trend is particularly obvious in the last 30 years of the period considered (see Fig 
ure 6.5). 
The number of days with ice is shown in Figure 6.6. Like the data for first and last ice formation, this 
parameter, too, clearly shows a declining trend in the last 30 years. The negative trend becomes even 
more apparent in Figure 6.7, which shows the variation of the 10-year mean values of the number of days 
with ice. Also the maximum ice thickness data (Figure 6.8) show the weak declining trend, but in this case 
it may be due to the increasing number of winters with weak ice formation during the past 30 years. The 
maximum ice thickness, measured in moderate or in strong to very strong ice winters, today reaches the 
same values as 56 years ago.